Controversies about marijuana have abounded since this reviewer started
medical school. Indeed, I can recall in my early years reading Grinspoon
and Bakalars Marihuana, the Forbidden Medicine and thinking how
a potentially useful medicine for some could be demonized by so many.
In the decade or so, research into marijuana has increased exponentially
and the debate in the Western world still rages on. Therefore this concise
volume focusing on marijuana and psychosis and depression, edited by two
very well known academic psychiatrists, is timely and highly relevant.

The first three chapters focus on basic and clinical neurosciences. Chapter
one begins with an easy to read neurochemistry review, looking at both
endogenous and synthetic cannabinoids. Next is neurophysiology from both
animal and human studies, especially the interactions with cannabinoid
receptors and various parts of the brains. It is tough reading and not
immediately applicable to most clinicians. Chapter three extends the preceding
chapter and focuses on human studies of cannabis: affective responses
to cannabis, effects on anxiety and cognition and the controversial amotivation
syndrome.

Chapter four reviews the mixed results of investigating the association
between cannabis and depression, a relatively new area of research. Whilst
there is some association between regular heavy use of cannabis and depression,
this effect may be very small.

The next four chapters focus on epidemiological and clinical trials looking
at the relationship between psychotic symptoms and cannabis. Verdouxs
studies form the base of chapter five: non-psychotic people can have transient
psychotic symptoms depending on baseline vulnerabilities, and such symptoms
occur after cannabis use. Chapter six challenges the concept of a specific
cannabis psychosis, pointing out that most of the research is old and
has methodological flaws. It is plausible that excessive cannabis use
in of itself can cause a clinical psychosis but it would be rare, due
to the large amounts needed. The authors emphasise that this is a difficult
area to investigate and it shows in the lack of major work in the last
ten years addressing this debate.

Chapter seven is excellent and of major relevance to mental health clinicians,
drawing on three epidemiological studies from Sweden, Netherlands and
New Zealand to conclude that cannabis has some potential causative factor
in the onset of schizophrenia. It clearly notes that cannabis is neither
sufficient nor necessary to cause schizophrenia and that it is merely
a component, whose strength as a causal factor remains to be seen. Chapter
eight describes well designed studies conducted only in the last ten years
that have confirmed cannabis use as an independent risk factor for psychotic
relapse in schizophrenia. This demonstrates how research can sometimes
lag behind clinical observation.

The next two chapters go back to the neurosciences with chapter nine
exploring the endogenous cannabinoid system and how it may help in investigating
schizophrenia. Like all other infant branches in psychiatry, evidence
is contradictory at times and clinical applications highly speculative.
Chapter ten looks at pharmacological trials of THC in healthy controls
and patients with schizophrenia. What this reader concludes is that it
is complicated and involves more than just dopamine!

Chapter eleven is excellent in outlining a motivational model of cannabis
use in psychosis that goes beyond a simple self medication hypothesis.
Chapter twelve reminds us of the lack of empirical evidence when it comes
to treating dual diagnosis patients. It discusses standard
treatment such as the cycle of change, motivational interviewing and harm
reduction, but does not offer anything groundbreaking. The last chapter
looks at long term cognitive effects of cannabis and how short term cognitive
deficits have been extrapolated to say cannabis has long term deleterious
effects. The authors conclude that there are many confounders preventing
proper investigation of the long term effects of cannabis.

The contributors of this volume come from a wide variety of backgrounds
and countries. It is good to see the strong presence of Australian authorship
and the impressive research in this field coming out of both New Zealand
and Australia. The chapters are of digestible length and easily accessible
for the busy clinician. The references were comprehensive and up to date.
For the clinician of whatever level of training, specialty or sub-specialty,
this book will provide some valuable knowledge and insight. For the trainee
preparing for examinations it provides more than enough up to date information
on a controversial issue. Given the continuing research in this area,
future editions would not be missed.